Polymer filaments play a major role in bacterial motility and morphology. Spirochetes, bacteria that swim by rotating helical flagella that are encased within a periplasmic space (the space between the inner and outer cell membranes where the cell wall material is located), are excellent model systems to study how elastic polymer filaments coupled to a bacterial cell wall can affect motility and morphology. Rotation of the flagella induces rotation and deformations in the cell wall. Because the flagella remain within the periplasm, the elasticity of the helical flagella competes with the preferred morphology of the cell wall. How this interplay between flagella and wall elasticity leads to total cell morphology and how forces developed by the flagellar motor drive motility is poorly understood. [unreadable] [unreadable] This grant will support the broadening of elastohydrodynamics to handle systems in which two or more elastic filaments are coupled together. This new mathematical framework will then be employed to model the morphology and motility of spirochete bacteria. Through study of the static shapes predicted by this model, this work will test the experimentally justified hypothesis that the flagella and cell wall are the dominant morphological determinants in spirochete bacteria and explore how the number and length of the periplasmic flagella affect these shapes. A detailed analysis of how this system responds to external forces and torques, as would be produced by the flagellar motor, will lead to an understanding of the dynamic shape changes that spirochetes undergo while swimming. Finally, the coupling of the resulting cell conformations to the viscous fluid environment surrounding them will be investigated to quantify the propulsive force generated by the rotation of the flagellar motor for many spirochetes and also explain the precession of the flat wave morphology in Borrelia burgdorferi. This grant will also support the experimental measurement of the bending moduli of the cell wall and the periplasmic flagella. [unreadable] [unreadable] [unreadable]